1. Field of the Invention
The present invention relates to an information recording apparatus for optically recording information, and, more particularly, to an information recording apparatus which can increase the recording capacity of a recording medium such as an optical disk and improve the reliability of recorded information.
2. Description of the Related Art
Recently, information recording/reproducing apparatuses, such as optical disk apparatuses, have been developed which record information on a recording medium such as a write once or erasable optical disk or reproduce information recorded on the recording medium. According to such information recording/reproducing apparatuses, an optical head which emits light is moved by a linear motor in the radial direction of an optical disk so as to face a recording or reproducing position on the disk. When the optical head reaches the target position, it emits light to record information on the optical disk or to reproduce information through photoelectric conversion of the reflected light from the optical disk.
A typical recording system for use in such optical disk apparatuses is the CAV (Constant Angular Velocity) system which keeps the number of rotations of the optical disk constant. This CAV system has merits of ensuring stable data recording and reproducing and shortening the required access time. According to this system, however, the number of clocks for data recording and reproducing or the frequency of data modulation and demodulation is constant irrespective of the location of target data on an optical disk, at the innermost track or at the outermost track. The CAV system therefore has a demerit of reducing the data recording density as the target position on the optical disk for data recording or reproducing approaches the outermost track.
There is another recording system for use in optical disk apparatuses, which uses the CLV (Constant Linear Velocity) system. This system provides a constant linear velocity and thus a constant recording density on an optical disk by reducing the number of rotations of the optical disk in accordance with movement of the position of an optical head on the optical disk from the inner track side toward the outer track side while keeping constant the number of clocks for data recording and reproducing or the frequency of data modulation and demodulation irrespective of the location of target data on an optical disk, at the innermost track or at the outermost track. This CLV system can increase the recording density on an optical disk and can therefore increase the recording capacity per optical disk. Due to the need to alter the number of rotations of an optical disk, the CLV system must wait for the rotational speed to reach the desired level. This undesirably results in a longer time for accessing to the target track for data recording or reproducing.
As a solution to the above shortcomings of the CAV and CLV systems, a constant linear density system has been developed which keeps the linear density on an optical disk constant. This system provides a constant recording density on an optical disk by changing the data transfer frequency at a recording/reproducing time in accordance with the position of an optical head on the optical disk while keeping the rotational speed of the disk constant. In other words, the constant linear density system provides a constant recording density by increasing the data transfer frequency in proportion to a change in position of the optical head on the optical disk or the recording position toward the outermost track.
The constant linear density system should increase the data transfer frequency in accordance with a change in the recording position toward the outermost track. Therefore, it should also satisfy severe data recording conditions on the outer tracks of an optical disk. In addition, due to the need to linearly increase the data transfer frequency in proportion to the recording position, the system needs additional hardware for controlling such a linear increase and its structure thus becomes more complex.